Fermenter temp indicative of yeast activity?

[joshbmace]

Hi all, still pretty new to homebrew - my fourth batch is fermenting right now. Previous three batches used WLP001 and I had no problem reaching FG. This time I decided to try WLP005 (British Ale Yeast). Within 24 hours things looked good; blowoff tube was bubbling and SG was dropping. However, in the last 3 days my gravity readings have sat at ~50% attenuation and hasn't budged. This is a highly flocculant strain, so I've been rousing the yeast by swirling the wort in the fermenter ~2x a day. I would normally figure that this was a straightforward issue with yeast health and/or unfermentable sugars from my mash. However, I have a brew bucket/FTSs setup; the temperature probe has shown the temperature slowly rising throughout the past 3 days, and the pump has regularly had to start to bring the temperature back down to my set point.

To me, this indicates continuing yeast activity, as the ambient temperature has not risen or fluctuated. But the unchanging SG readings contradict this. Anyone have any theories or experience to explain this?

*caveat - I am using a refractometer for gravity readings, however I have determined my specific instruments' correction factor and I'm using an excel calculator to account for ethanol in the sample*

 

[D.B.Moody]

Well, to say the least, I have a much more casual approach to brewing than you do. But reading your post suggests to me that your swirling the wort twice a day may keep things suspended, or put stuff back in suspension. Wouldn't that keep the refraction readings from dropping?

 

[Yooper]

With a refractometer, the readings are meaningless when alcohol is in the mix. . That’s because alcohol skews the refraction of light in a sugar solution.

But.....if the refractometer is reading the same, it means that fermentation is finished. You can use a refractometer correction tool in brewing software to guesstimate what the SG could be, or you could grab a hydrometer reading. Either way, the reading right now gives no clue at all to what the actual SG reading is.

 

[Yooper]

Oh, and stop swirling the fermenter- as you are not helping the yeast and seemingly messing with your readings somehow. Oh, and double check your refractometer with plain water- if it’s unchanging, that’s a clue that fermentation is finished but something is not adding up here.

 

[mcmeador]

I know you mentioned your room temp hasn’t fluctuated, but do you have your temp control set to match the room temp?

—————
Follow my homebrew-themed Instagram!
@mcmeador

 

[tracer bullet]

I'd say an increase in temp in the fermenter, all else being equal, would indicate yeast activity. However, I'd be skeptical all else is equal. Even in the medical device manufacturing clean room where I work we fluctuate in temps, and of course if I were to have beer out there (I wish) it'd show the same. You could also have outgassing, but pv=nrt it should mean the temp lowers. Anyhow I'd suggest being skeptical that it isn't still being influenced from the outside.

I also highly suggest a hydrometer. I know that a corrected refractometer is in theory OK, and that of course a stable reading probably means just that. And that a hydrometer means some beer disappears, and if you're really picky means you might have to supply CO2 or crack a stopper and let O2 in, in order to allow beer to go out. But to me a hydrometer is my official way of telling my final gravity. As a small bonus you get to taste test your beer afterwards, which too can be a tool in addition to just being fun.

What did you brew, how many gallons and how much grain / starting gravity did you get? Don't have to have a ton of detail but an idea. A Russian Imperial Stout could end at a gravity that's way higher than you expect if you are used to brewing lighter more "normal" beers.

 

[Bramling Cross]

I don't know my White Labs strains very well, but that's the Ringwood strain, right? If so, that strain has a legendary reputation for being temperamental. If memory serves, it can be a bit temperature sensitive. There are, however, plenty of brewers that have learned how to bring it to heel, hopefully someone will pass by and help you out. I'm not that guy, though.

At any rate, know that you're not the first sailor to crash upon Ringwood's rocks.